1. Field of the Invention
This invention relates to plug valves having a transverse cylindrical plug member rotatable to open and close a fluid transmission conduit and especially related to plug valves used for the transmission of liquids and gas in the performance of oil field services.
2. Description of the Prior Art
Conventional plug valves have been employed in oil field service applications, such as cementing, fracturing and acidizing. Conventional plug valves comprise a cylindrical plug member disposed transversely to a fluid transmission conduit and rotatable to both open and close the fluid transmission conduit. Such conventional plug valves are generally positioned within an external housing or body attached within the fluid transmission conduit or flow line. A separate tapered insert, normally comprising two tapered or conical halves, is generally positioned between the cylindrical plug and the body within a tapered body bore extending transverse to the fluid transmission line. In order to render such conventional plug valves suitable for gas service or for use with corrosive fluids, a liner fabricated from a inert material, such as polytetrafluoroethylene, is generally inserted between the plug member and the tapered insert. In such gas applications, lubrication of the inner face between the cylindrical plug member and the inner bore of the tapered insert is difficult, if not impractical. A conventional plug valve used in oil field service applications is disclosed in U.S. Pat. No. 3,133,722.